Issue with drag and drop functionality for .jar files in JavaFX application

Issue with drag and drop functionality in JavaFX application

I'm currently working on a JavaFX application and trying to implement a drag and drop functionality. I have a pane in my UI where I want users to be able to drag and drop files, specifically .jar files. However, I'm encountering an issue where the cursor shows a cancel sign when I drag a file over the pane, and the drop event is not triggered.

I've tried various approaches, including setting the onDragEntered, onDragExited, onDragOver, and onDragDropped event handlers for the pane. I've also set the TransferMode to COPY and verified that the dragboard has files. However, the desired behavior is not working as expected.

Here is my FXML file:

<?xml version="1.0" encoding="UTF-8"?>
<?import java.net.*?>
<?import javafx.scene.control.*?>
<?import javafx.scene.layout.*?>
<AnchorPane maxHeight="-Infinity" maxWidth="-Infinity" minHeight="-Infinity" minWidth="-Infinity" prefHeight="400.0" prefWidth="600.0" xmlns="http://javafx.com/javafx/17.0.2-ea" xmlns:fx="http://javafx.com/fxml/1" fx:controller="com.example.detector.Controller">
<stylesheets>
<URL value="@styles.css" />
</stylesheets>
<children>
<Pane fx:id="dragDropPane" layoutY="-3.0" prefHeight="349.0" prefWidth="600.0" />
<Button layoutX="545.0" layoutY="361.0" onAction="#onOpenButtonClick" text="Open" />
<TextField fx:id="pathText" layoutX="14.0" layoutY="361.0" prefHeight="25.0" prefWidth="515.0" />
<Label layoutX="255.0" layoutY="192.0" text="Drag .jar file here" />
</children>
</AnchorPane>

And here is my controller code:

import javafx.fxml.FXML;
import javafx.scene.input.DragEvent;
import javafx.scene.input.Dragboard;
import javafx.scene.input.TransferMode;
import javafx.scene.layout.Pane;
import java.io.File;
public class Controller {
@FXML
public Pane dragDropPane;
@FXML
public void initialize() {
dragDropPane.setOnDragEntered(event -> {
if (event.getGestureSource() != dragDropPane && event.getDragboard().hasFiles()) {
dragDropPane.setStyle("-fx-border-color: blue; -fx-border-width: 2;");
event.acceptTransferModes(TransferMode.COPY);
}
event.consume();
});
dragDropPane.setOnDragExited(event -> {
dragDropPane.setStyle("-fx-border-color: transparent;");
event.consume();
});
dragDropPane.setOnDragOver(event -> {
if (event.getGestureSource() != dragDropPane && event.getDragboard().hasFiles()) {
event.acceptTransferModes(TransferMode.COPY);
}
event.consume();
});
dragDropPane.setOnDragDropped(event -> {
Dragboard dragboard = event.getDragboard();
boolean success = false;
if (dragboard.hasFiles()) {
for (File file : dragboard.getFiles()) {
// Process the dropped file
System.out.println("Dropped file: " + file.getAbsolutePath());
}
success = true;
}
event.setDropCompleted(success);
event.consume();
});
}
}

I'm unsure why the drag and drop functionality is not working as expected. I appreciate any insights or suggestions on how to resolve this issue. Thank you!

I copied the initialize method contents into the start method of a new app and added the bits that would allow it to display and run and it worked for me with no issue. (JavaFX & JDK 20 on Win 11).

I dropped files from the file explorer into the app window and they were named in the system out, as per the drop handler code.

Output

javafx.scene.input.DragEvent[source=Pane@6b2cc6e[styleClass=root]]
Dropped file: C:\Users\<username>\OneDrive\Documents\flight.txt

Code

import javafx.application.Application;
import javafx.scene.Scene;
import javafx.scene.input.Dragboard;
import javafx.scene.input.TransferMode;
import javafx.scene.layout.Pane;
import javafx.stage.Stage;
import java.io.File;
public class CopyHandler extends Application {
public static void main(String[] args) {
launch(args);
}
@Override
public void start(Stage primaryStage) {
Pane dropPane = new Pane();
dropPane.setPrefSize(600, 400);
dropPane.setOnDragEntered(event -> {
System.out.println(event);
if (event.getGestureSource() != dropPane && event.getDragboard().hasFiles()) {
dropPane.setStyle("-fx-border-color: blue; -fx-border-width: 2;");
event.acceptTransferModes(TransferMode.COPY);
}
event.consume();
});
dropPane.setOnDragExited(event -> {
dropPane.setStyle("-fx-border-color: transparent;");
event.consume();
});
dropPane.setOnDragOver(event -> {
if (event.getGestureSource() != dropPane && event.getDragboard().hasFiles()) {
event.acceptTransferModes(TransferMode.COPY);
}
event.consume();
});
dropPane.setOnDragDropped(event -> {
Dragboard dragboard = event.getDragboard();
boolean success = false;
if (dragboard.hasFiles()) {
for (File file : dragboard.getFiles()) {
// Process the dropped file
System.out.println("Dropped file: " + file.getAbsolutePath());
}
success = true;
}
event.setDropCompleted(success);
event.consume();
});
primaryStage.setScene(new Scene(dropPane));
primaryStage.show();
}
}